But amid the chaos, a classified and highly sensitive operation by Americans and Chileans was underway on the outskirts of Santiago, the Chilean capital, to secure weapons-grade nuclear material -- the kind terrorists are keen to get their hands on.

"Nightline" was in Chile for several days before the quake struck documenting the work of the National Nuclear Security Administration's Global Threat Reduction Initiative (GTRI) team.

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Loose Nukes

"This operation is an effort to secure nuclear material that terrorists could acquire to make a nuclear device, as well as radiological material that they could acquire to make some kind of dirty bomb," said Andrew Bieniawski, the NNSA assistant deputy administrator who oversees collecting and securing vulnerable nuclear material from civilian facilities around the world.

In Chile, the team has come to pack up the highly-enriched uranium from two research reactors that no longer need it. The HEU will be shipped back to the U.S. where it will be stored in a secure, classified facility and converted to non-weapons grade material.

So-called "fresh" or unused highly enriched uranium is a terrorist's dream. Because it doesn't emit high levels of radiation, it's easy to pick up and run with. It only takes a small amount -- about the size of a grapefruit -- to make a nuclear weapon.

"When the material is no longer here, terrorists cannot acquire the material [and] the country is safer. That's the bottom line," said Bieniawski.

There is reason to worry. Nearly 40 countries around the world have highly-enriched uranium or plutonium -- ranging from multiple tons to a few kilograms. Total world stockpiles are enough to make more than 200,000 nuclear bombs.

Much of the material is not completely secure. According to the International Atomic Energy Agency, there were nearly 250 reported thefts of nuclear or radioactive material worldwide from June 2007 to June 2008.

Three years ago, armed men breached security at a nuclear reactor in South Africa, which contained enough material for 30 nuclear weapons.

And this past February, peace activists jumped a fence at a NATO air force base in Belgium where the U.S. reportedly stores an arsenal of nuclear bombs. They didn't get inside the bunker where the nukes were, but they did wander around the "highly secure" base for as long as an hour before being arrested.

The security breach was particularly troubling because al Qaeda terrorist Nizar Trabelsi was convicted in 2003 of plotting to drive a car bomb into the same base after meeting with Osama bin Laden.

"We are more than redoubling our efforts to secure this material, to make sure that any individual or any groups of individuals can't just jump a fence or two and get very close to this material," said Secretary of Energy Steven Chu, who is in charge of overseeing nuclear non-proliferation efforts.

Chu, who won the Nobel Prize for physics, said it's "a lot easier than it used to be" to make a nuclear weapon.

"The hardest part of making a bomb is to get the material," he said. "That's why it's so imperative that we get that material locked up tightly in a way that essentially like a super Fort Knox, where terrorists simply cannot get at. It would be devastating if terrorists got their hands on this material, set it off in a major metropolitan area anywhere in the world."

Obama on Nuclear Security

The top-secret mission in Chile unfolded as heads of state from 47 countries prepared to come to Washington, D.C., for the first-ever nuclear security summit, beginning April 12.

Securing vulnerable nuclear material from civilian sites around the world has been a priority for the Obama administration.

At the start of his term, President Obama pledged to reduce nuclear arsenals around the world and this week, the administration announced changes to U.S. nuclear policy, which will restrict the use of nuclear weapons. The new policy includes a controversial pledge to refrain from using nuclear weapons to attack any country that is in compliance with the Nuclear Non-Proliferation Treaty, even if that country has attacked the United States with chemical or biological weapons.

In Prague last April, the Obama administration announced a new international effort to secure all vulnerable nuclear material around the world within four years.

The NNSA has been working behind the scenes to reach that formidable goal. It has upgraded security at hundreds of sites, converted 60 reactors to non-weapons-grade fuel, and helped retrieve more than 150 bombs-worth of nuclear material from sites in dozens of countries. The mission in Chile is one part of that effort.

It's all part of Obama's larger agenda to "prevent the spread of nuclear weapons" and enhance global security.

Earthquake Upends NNSA Mission

As part of their mission in Chile, the NNSA team -- working closely with the Chileans -- removed fresh uranium as well as the highly-radioactive spent uranium from the heart of the reactor.

"As long as there is highly enriched uranium, there is always a concern that something that could happen to a facility," said Bieniawski.

Armed guards secured the perimeter as every bit of the material was weighed so each microgram could be accounted for on every step of the journey. After 10 days, the material was packed and ready to go.

The next day, the earthquake struck. No one on the team was hurt, but suddenly the mission had become infinitely more complex.

"There is no power in this facility here," Bieniawski said. "The toilets aren't really working very well. ... We are walking down the halls with flashlights. People are basically tripping down the stairs because there is no emergency backup lighting."

The port the team intended to ship the nuclear material from suffered major damage from the quake, forcing them to chart a whole new route.

"We have never been in a situation where we have had an earthquake and had to adapt to a situation like this," Bieniawski said.

Hazardous Journey to the Port

At dusk, armed guards stood watch as the cargo was loaded on to trucks for the overnight journey to the port.

"The truck over here to my right has the most attractive material from a terrorist perspective," Bieniawski said. "It is fresh highly enriched uranium, which means you can just hold it in your bare hands, so our biggest concern is to make sure this container is protected."

The riskiest part of the mission is moving the nuclear material. To ensure there was no sabotage prior to departure, dogs sniffed for explosives, but not everything went smoothly: The Chilean police escort arrived more than an hour late, and another tremor rocked the new destination port of Valparaiso. The team decided to move forward.

For the entire five-hour drive, the nuclear material was escorted by a Chilean SWAT team.

Police on motorcycles led the way in the race against time -- and terrorists.

The team worked through the early hours of the morning, loading each container onto the ship one by one, as the sun slowly rose over the port of Valparaiso.

Nearly 12 hours after the caravan began its journey, the last container was loaded.

"We are pretty exhausted, but at the same time pretty exhilarated that we have done what we came to do," said Bieniawski. "As a result of this, the world is safer."

Two weeks later, the boat carrying the last of Chile's nuclear material arrived safely at the Charleston Naval Weapons Station, officially making Chile the 18th country the NNSA has cleared of all weapons grade nuclear material. Seventeen other countries such as Brazil, Libya, Romania, Turkey have already been cleared, but there's at least 19 more to go.

Click here for more information on the NNSA, and click here to visit the Web site for the Nuclear Threat Initiative.